Transcript:

Electrons are what are called spin half particles. Spin half means that the electron needs to rotate two times—which means not 360 degrees, but two times, so 720 degrees—for it to come back to its original position. It's not a very good definition, but I can show you an example.

So, let's say this is an electron. This is an orange, not an electron. I'll show you what spin half means. So you take this, and you make one rotation like this. You see, you're rotating around your elbow. So you are here, and you're no longer back to the original position, right? But you can make one more rotation, and now you come back to where you started. So you go one this way, and you're all twisted up; and you go one this way—back to where you started.

This—the ability to go two rotations and come back to its original position—is what is actually spin half. And this thing, this two-rotation business, can only happen in space in which there are three physical dimensions that are expanded. So, in 3D space, you can have this spin half business going on.